Control system



June 17, 1941. H. T. SPARROW CONTROL SYSTEM Filed May 12, 1937 3Sheets-Sheet 1 FIG. I.

ll 3 m "7 INVEN TOR. HUBERT T. SPARROW BY June 17, 1941. SPARROW2,245,730

CONTROL SYSTEM Filed May 12, 1937 3 Sheets-Sheet 2 FIGS.

INVENTOARJ HUBERT T. BY

ATTORNEY June 17, 1941.

H. T. SPARRQW CONTROL SYSTEM Filed May 12, 1937 3 Sheets-Sheet 3INVENTOR.

HUBERT T. SPARROW ATTORNEY Patented June 17, 1941 UNITED STATES PATENTOFFICE CONTROL SYSTEM Hubert T. Sparrow, Minneapolis, Minn., assignor toThe Brown Instrument Company, Philadelphia, Pa., a corporation ofPennsylvania Application May 12, 1937, Serial No. 142,115

31 Claims.

The present; invention relates to an improved fuel combustion controlsystem and more particularly to such a control system having safetymeans for distinguishing between normal conditions of combustion andabnormal conditions.

An object of the present invention is to provide a system of the classdescribed wherein means are provided for distinguishing between anactual condition of combustion and a simulated condition of combustion.

A further object of the invention is to provide a fuel combustioncontrol system having means for automatically supplying and igniting thefuel wherein further fneans are provided for preventing the operation ofthe fuel supplying and igniting means if abnormal conditions exist.

A further object of the invention is to provide such combustion checkingmeans which operate upon the occurrence of an abnormal condition evenafter initial combustion ha taken place to shut down the fuel supplymeans.

' Another object of the invention is to provide a combustion controlsystem of the class described in which the combustion conditions in aplurality of fuel fired furnaces may be controlled by means of a singlecontrol system.

In combustion control systems which have been proposed heretofore,various means have.

been employed for determining if combustion conditions are proper, andwhether combustion actually, takes place, one such means comprisinganelectrode which extends into the flame of the burner and'which is soconnected in the system as to provide a conductive path of relativelylow resistance to. ground through the flame. The variation in theelectrical conductivity-of this path to ground when a flame is presentand when a flame is not present is commonly employed to change the biason the controlgrid of an electronic device for controlling the thermalsafety switch. Since there is a possibility that a low resistance pathmay be set up from the electrode to ground through] other agencies thanby means of the flame, for example, a low resistance path which may beestablished between the flame electrode and ground by reason ofcarbonization, by accidental touching of the electrode to ground, or byotherabnormal conditions simulating combustion, provisions have beenmade indevices of the prior art for preventing the fuel supplying and,ignition means from being turned on when such an abnormal} conditionexists.

An abnormal condition of this character simulating combustion may ariseafter the system is already in operation and, hence, it is desirable toprovide means for distinguishing between this abnormal condition andactual combustion while the system is in operation. For example, in athermostatically controlled house heating system, if the control systemis insensitive to the presence of the flame after initial ignition ofthe latter, the fuel feeding means will be operated continuously as longas the room thermostat is closed. If the flame should then beextinguished, the furnace will be flooded with atomized fuel and ahighly explosive mixture of the latter will be permitted to accumulate.

In a combustion system in which a plurality of burners operate togetheras for example, for heating in unison and supplied with a common fuelline, it is important that an abnormal or dangerous condition of any oneof the burners is guarded against. In such a system failure of any oneof the burners to ignite may result in an explosion.

The various features of novelty which characterize my invention arepointed out with particularity in the claims annexed to and forming apart of this specification. For a better understanding of the invention,however, and the advantages possessed by it reference should be had tothe accompanying drawings and descriptivev In Figpl of the drawings agas burner l is "shown as supplied with gas through conduit 2 and theflow of gas to the burner is controlled by an electrically operated orother suitable valve 3. A pilot burner 4 is provided which is controlledby an electrically operated or other suitable valve 5, and means'areprovided for igniting the pilot flame including a pair of electrodes 6which are connected to the terminals of a sec ondary winding I of anignition transformer. 8

having aprimaryfwinding 9 which is adapted to be energized from thealternating current supply lines L and IF.

The fuel valve operating circuit of my control in this positionelectronic valve 36 is a and functions both as a rectifier to supply asource pulsating direct current flows from the diodes 34 having afilament cathode 44 connected by consystem is controlled by means of thethermostat In which may be located in a room or space to be. heated. Thethermostat l may be of any suit able construction and includes abimetallic element I connected by means of conductor l2 to lessdiagrammatically in the drawings, this switch comprises a stationary arml8 and a movable arm I!) biased for movement away from arm |8 butnormally held in engagement with the latter by means of a bimetallicelement 26. Element .26 is rigidly secured at one end to a block 2| andis arranged to be heated by a coil 22 when the latter is energizedthrough a circuit which will later be described. Upon energizatlon ofcoil 22 fora predetermined period of time, ele- 1 ment 26 will be warpedsufliciently in the clockwise direction to permit arm l9 acting underspring or other bias to separate from switch arm I6 thereby interruptingthe circuit including thermostat Hi. The switch 5 will remain lockeduntil manually returned to its normal closed position. The transformerl1 which supplies power for the control system is a combination step-upand step-down transformer and comprises the line voltage primary winding6, low voltage secondary windings 23 and 24, and high voltage secondarywindings 25 and 26; The low voltage secondary winding 23 is connected byconductors 21 and 28 to the heater filament '29 of an electronic valve30 and supplies ener g current thereto. The

duplex-diode-triode type of direct current for gridbiasing means and asan amplifien The valve 36 includes an anode 3|,.a grid 32, a cathode,33, a pair of diodes 34, and the heater filament 29. The transformersecond-1 ary winding 25 is connected by conductors 35 and 36 in acircuit including the cathode' 33 and the diodes 34 which may beconnected together since it not necesary in the present case to havefull wave rectification. This circuit may be traced.

from the diodes 34., cathode 33, conductor 31, a condenser 38, conductor35, through the secondary winding 25, and conductor 36 to the diodesSince only half wave rectification is obtained with the diodes connectedas shown in Fig. 1,

to the cathode 33 and this pulsating current isimpressed across theterminals of the condenser 38 which operates to filter out thepulsations. It will be noted that the cathode 33 is connected to thepositive side of the condenser; and that the negative side of the latteris connected through conductor 39, resistors 46- and 4|, and conductor42 to the grid 32. The tendency of the voltage produced through therectifying action of] the diodes 34 and cathode 33 is thus seen to biasthe grid 32 negatively. Y A" second electronic valve 43 is provided,which valve may be a conventional full wave rectifier,

ductors 45 and 46 with a suitable portion of the transformer secondarywinding 24 and receiving energizing current therefrom. The anodes 41 and48 of the valve 43 are connected by conductors. 48 and 50 with theterminals of the transformer secondary winding 26', and therectifiedplate our- 7 in detail, additional current will be caused toflow rent of the valve 43 is connected across the terminals of afiltering condenser 5|. A center tap on the secondary winding 26 isconnected by a conductor 52 to one terminal of the condenser 5| and theother terminal of the latter is connected to the filament cathode 44 sothat a direct current and the rectifier valve 43 is to raise thepotential of the grid 32 with respect to the cathode 33. It will thus beseen that two sources of direct current voltage are provided, one ofwhich is connectedso as to bias the grid negatively, and the other ofwhich when connected to the grid, tends toreduce said bias.

As shown in Fig. 1, a plurality of relays desi nated as 66, 6|, 62 and63 are employed in the control system. The relay 60 .is a sensitivediffer ential relay which is employed primarily for distinguishingbetween normalconditions of combustion and conditions which simulatecombustion. The main function of the relay 6 I, which is controlled bythe relay 60, is to check the operation of the system before the fueligniting and fuel feeding means are permitted to operate, and aftercombustion has been established, to bring about the desired operatingconditions. Energization of the relay 6| will result in the closingof anenergizing circuit to the relay 62 and, if I only normal conditions ofcombustion are present, the relays 66 and 6| will be. deenergized and anoperating or combustion producing condition of' the system may beestablished. 'De-energizatio'n ofthe relay 6| resultsin the closure ofan energizing circuit to the relay- 63 which functions to establish theconditions necessary for combustion.

The three relays BI, 62 and'63 are alternating current relays and areenergized through a circuit from the transformer secondary winding 24.

The relay 66 is a direct current relay and is included in the outputcircuit of the electronic valve which are operatively associated with abalanced armature 66. This armature is pivoted for rota tion at 61, apoint intermediate its ends,- and carswitch blade 10 which is adapted toengage a "cathode circuit and the winding is connected in the anodecircuit of the electronic valve 36 so contact The winding 64 isconnected in the that,- when the valve is conductive as it normally willbe, the same current flows through both windings and the winding 65 iswound with more turns -than the winding 64. In consequence, when nor-.mal operating current flows through both windings, the winding 65 willbe stronger magnetically than the winding 64 andthe armature 66wi11 berotated in a clockwise direction. Under abthrough the winding 64 and thelatter will become stronger magnetically than the winding 65.

As illustrated in Fig. 1 rotation of the armature Y 66 in a clockwisedirection moves the armature switch blade 16 into engagement with thecontact H, which engagement results in the closure of an energizingcircuit to the relay 6-| from transformer winding 24 over conductor 45,switch arm Relay 6!! comprises two coils 64 and 65' 19, contact 1|, awinding 12 of relay 8 l, conductor 19 to the opposite side oftransformer winding.

Winding 12 is operatively associated with three switch arms 14, 15 and16 which are spring biased toward the right, and when the relay winding12 is tie-energized, the arms 14 and 16 engage contacts 11 and 18,respectively. When the relay winding 12 is energized, the arms 14, 15,and 19 move into engagement with contacts 19, 89, and Bi, respectively.w Y

The relay 62 comprises a winding 82 which is operatively associated witha switch arm 83. This arm is similarly biased toward the right and, whenthe winding 82 is de-energized, is in engagement with a contact 84.

The fourth relay 83 comprises a winding 85 which is operativelyassociated with three relay arms 88', 81 and 88. These arms are'alsobiased towards the right and are adapted to be moved into engagementwith contacts 89, 99 and;9i upon energizationofthe relay winding 85.

the left end terminal of the" transformer secondary winding 24,conductor 45, conductor 95, contact 19, switch blade-14, conductor I95,conductor I99, relay winding 82, conductor IN, and conductor 13, back tothe other terminal of the transformer secondary winding 24. Theestablishment of this energizing circuit for relay 92 causes the switchblade 83 to be moved into engagement with the contact 94, and suchengagement establishes a holding circuit for the relay 62 which may betraced from conductor 45, conductor 95, switch blade 83, contact 94,conductor I99, relay winding 82, conductor I9I, conductor 13, and thetransformer secondary winding 24 to the conductor 45.

At the same time that the switch blade 83 moves into engagementjwith thecontact 94 it When the temperature of the room or space to be controlledfalls below thevalue it is (16-,

sired-to maintain, the thermostat l9 operates to move the SwitchbladeI3- into engagement, with the contact [4 resulting in closure of anenergizing circuit fto the transformer; primary'wind- .ing and thereby.energization of the transformer secondary windings. As soon as thecathode .89

of the tube 38 becomes heated, a direct'current voltage appears acrossthe terminals of the condenser 38 which, because of the connectionspreviously described, causes a negative biasing voltage to be applied tothe grid 32 of the tube 39.

In a similar manner, as soon as the cathode 44 of the tube 43 becomesheated, a direct current moves out of engagement with the contact 84,and sincethe previously traced connection between the grid 32 andtheqpositive side. of .the

condenser {5i depended upon the engagement of switch arm so ,with thecontact 84,- the grid 32 is nowsubjected. only; to the 1 negativebiasing (voltage appliedlacross condenser 38. .;The re'- suit is thatthe gridfpotentjial now-sufficiently and s'i-nce no piate flows throughthe relay-windings 54-' and 85, the latter are de-.

nergizes thelswitflhnbiade 19 moved out .of

engagement with the contact 1i.

When the switch blade 19 is so. moved out ofengagement with the contactfit the relay winding ,12is de-energized and the switch blade 18- againengagesthe contact 71 to close an energizing circuit to-the relaywinding 8*. This circuit voltage appears across the terminals oi the. T

condenser 5!. As previously pointed out, the negative terminal of thecondenser 51 is connected together with the positive terminal ofcondenser 38 to the cathode 39.

When the system is initially energized, the various relays are in thepositions shown in Fig. l, and the grid 32is connected to the positiveside of condenser 5i through a circuit including grid 82, conductor 42,resistance 4|, c'onductor92, re-

sistance 98, contact 84, switch arm 83, and con-v doctor 95 to thepositive terminal of the condenser 5i. The result of this connection ofgrid 82 to the positive terminal ofithe condenser 5i, which has avoltage applied across it which greatly exceeds the voltage across thecondenser 38, is that the grid 92 is subjected to a positive" voltagewhich-reduces the negative biasing. action of the condenser 38sufficiently to cause a current to flow between anode 3i and cathode 88.The circuit path through which such anode circuit flows may be tracedfrom the positive terminal oil the condenser 5|, conductor 95,resistance 98, relay winding 85, conductor 91, anode 3i, cathode 33,conductor 31, conductor 93, relay winding 84 and conductor 99 to thenegative side of the condenser 5i. Y

This how or current through the anode circuit including the-relaywindings 64 and 65 is e'fiective to cause the armature 68 to rotate inisenergized only because the previously mentioned holding circuit forthe'relay winding 82 has been closed, and may betraced from the lefthand end of transformer secondary winding 24, conductor 45, conductor85, switch blade 98, contact 94; switch blade 'id contactl'l, conductorI92, heating element 22, conductor l98, relay winding 85, conductor H88,and conductor 19- baclr to the other side of the transformer seca ondarywinding 24. The energization of relay 88 7 causes the relay arms 86, 91and 88 to be moved into engagement. with the contacts 89, 89 and .84,respectively. The engagement of switch blade 88 with contact 89 closes aholding circuit for the relay winding 85 from one end of the transformersecondary winding 24, conductor 45, conductor 95, switch blade 83,contact 98, conductor i115, contact 89, switch blade 86, conductor I92,

' heating element 22, conductor I93, relay winding 85, and conductorsllll and 13 back to the other side of the transformer secondary wind-' aclockwise direction and to move the switch blade 19 into engagement withthe. contact 1i,

. and to thereby close the previously mentioned energizing circuit tothe relay 5|. The relay '1 arms 14, 15 and 18 are then moved intoengagement with the contacts 19, 89 and 9 I, respectively.

The movement of arm 14 into engagement with contact 18 establishes anenergizing circuit through the relay 62 which may be traced from ing'24. The establishment of the holding circuit just traced functions torender the energization of vrelay winding independent of relay 8i sothat when the relay 8i becomes re-energized, as subsequently takesplace, the relay 63 will remain energized. It is pointed out, however,that" the energizing and holding circuit for relay winding 85 includesthe heating element 22 of the thermal safety switch iti so that as soonas the relay winding 85-is energized the heating element of the thermalsafety switch begins to heat the bimetallic element 29.

When the relay 85 is energized, the resulting movement of the switchblade 88 into engagement with the contact 9! results in theestablishment of the following circuit through the operating means forthe valve 5, which controls the supply of fuel to the pilot burner:from. supply line L conductor i98, switch blade 88, con- ,winding Ewhich is applied to 'fuelvalve, however, until a check has been mademeans, and conductors ma, m9 and no to the supply line L. Theestablishment of this circuit causes the valve controlling the pilot tobe opened with the result that fuel is fed thereto. At the' same time,-the ignition transformer 8 is energized through a circuit includingsupply line L conductor I06, switch blade 88, contact 9!, conductor I01,switch blade l5, contact 78, the ignition transformer primary winding 9and conductors H I and H to the supply line L. This energization of theprimary winding of the ignition transformer 8 causes a high voltage tobe induced across the terminals of the secondary produce a spark acrossthe electrodes 5.

Combustion will now take place if conditions are proper and the controlsystem will subsequently operate to open the main fuel valve and tode-energize the ignition transformer. As

I ant-moving into engagement of switch arm 87- soon as a flame appearsat the pilot, a circuit is I established through the flame whichoperates to reduce the negative bias on the grid 82 to render the tubeconductive. The plate current conducted bythe latter energizes the relay66 which operates in the manner previously described to rte-energize therelay 56." As will he described hereinafter, re-energization of therelay Gl results in operation of'the main fuel valve "andde-energization of the ignition means.

The means for reducing the negative bias on the grid 32 for renderingthe tube 30 conductive and subsequently causing opening of the main asvalve 3 includes an electrode H2 which is insulated from the burner andextends into the pilot flame. This electrode is connected throughconductor 1 l3, protective resistance H 3, and conductor $12 to the grid32. The pilot supply pipe is connected toground as indicated at 5 andthe positive side of the condenser is connected 'to ground as indicatedat H6. When a flame of lower resistance than the air gap'appears at thepilot by reason of the same being lighted, an electrically conductivepath is established be tween the grid 32 and the positive side of thecondenser 5|. This path is of low enough resistance to drive the gridsuiiiciently positive to render the tube 38 conductive. The resistor H lis'of comparatively low value and is provided to pref ,ventthe grid frombeing subjected to too high the presence of a flame Y the grid bias notbeing sumciently negative that'- the system is too sensitive. Bycuttingout ref-sistor 68 it is necessarythat there be a material reduction inthe resistance in the circuit between I the grid 32 and the positiveside of the condenser on the insulation resistance of the system. Re-

with contact 30, the resistance 50 is shunted out through a circuit fromone endof resistance 46, conductor 92, contact 98, switch blade 81 tothe opposite side of the resistor. It isthus seen that until relay 83 isenergized, the resistance between the grid and the negative side of lthe condenser 38 is much greater than after energization of this relayso that during the initial stages of operation of the system the grid isbiased less negatively, I I

The advantage obtained in so biasing the grid lessnegatlvely during theinitial stages of operaticn and increasing this bias later on is thatif, through insulation leakage or due to a low resistance between theelectrode H2 and the pilot burner d, there is a path of comparativelylow resistance between the grid and the positive side.

of the condenser 55, which side is the grounded side, the grid bias willremain sufiiclently low so that the tubeilfl will be conductive. Sinceit is necessary for the tube 3B to be non-conductive before the relay 63can be energized, the latter will not be energized in the event ofexcessive insulation leakage. As soon as the resistance 36 is shuntedout, however, the negative bias on the grid 32 is increasedso that inorder to again reduce the grid bias suiiciently to render the tube 38conductive, a substantial decrease in resistance between the grid andthe positive side of the condenser 5i is required,

Inthis manner a check is' made on the insulation resistance of thesystem while at the same time provision is made against a faulty checkof being made by virtue of iii such as in the event of a-flame bridgingthe a voltage if the electrode should accidentallybe connected directlyto ground, and functions to limit the flow of grid current in theelectronic valve 30 to a safe value.

I When the tube 30' is thus rendered conductive, the resultingenergization of relay Stand con sequent energization of relaySi-operates to move I the switch arms. 1d, 75 and 16 into engagementwith the contacts is, 80 and 8!, respectively;

Movement of the arm 86 out of. engagement with the contact 78 causes thepreviously traced cir-- I cuit through the primary of theignition-'trans-- former to be interrupted with the result that theignition means is tie-energized. At the same time movement of the arm 16into engagement with contact 8! establishes an energlzinglcircuit to thevalve actuating means 3 from supply line L conductor-3N5, switch blade88, contact 9!,

ductor Ill, the co'ntrolvalve 3, conductor 8,

conductor I01, Switchblade-l6, contact M, conconductor I09, andconductor H0 to the supplyline L. The main f'uel'valve 3 'isthen openedI and fuel is admitted to the burner l, which fuel is subsequentlyignited by the pilot flame.

gap between the pilot and the electrode M2.

Moreover, thislnsures recycling in theeveht of pilot flame failure, thatis, immediate closure of the main fuel velvet and re-energization of theI ignition transformer t to re-light the pilot flame and to subsequentlyopen the main fuel valveu This insurance is had since even thoughtheelectrcde-may have become somewhat carbonized in use, the resistancebetween'the electrode and ground by virtue of the carbonization willordinarily. be too high to maintain the bias su fliciently low to permitthetube 36 to become con-V ductive.

It will be. noted that the connection was,

the grid 82 and the positive side of thecondenser- 5} includes theresistance ll.

nected through this resistance to relay contact S6, and since it isextremely diflicult to adequate- The grid is conly insulate parts of a,relay without impedingtheir proper function, it is desirable that theresistance 4! be of rather large value, forex- The system is notpermitted to open the main ample, of the order of 50 megohms. There is,then assurance that anypath betweenthe grid and the grounded highpotential side of the system, other than through the electrode l I 2,will be of suchhigh resistance as to not appreciably raisethe-potentialof the grid. I I

The re-energization of relay 6| with the resultant movement of arms 14and 15 into engagement with contacts 19 and 80, respectively,establishes a new holding circuit for relay winding 85 which does notinclude the resistance 22 of the thermal safety switch I but shunts thatresistance. This circuit may be traced from one end of the secondarywinding 24, through conductors 45 and 95, contact 19, switch blade 14,conductor Hi5, contact 89, switch blade 86, conductor H02, contact 80,switch blade I5, conductors H9 and H03, winding 85, and conductors Illiand 13 to the other endof secondary winding 24. Short circuiting of theresistance 22 in this manner operates to render the thermal safetyswitch I5 inopera-.

tive and the system will then remain in operation as long as normalcombustion conditions exist and the thermostat I0 is in closed position.

As illustrated in Fig. 1, an additional safety feature has been providedfor delaying the action of the ignition cut-01f means until there is acer-' tainty that a steady pilot flame is burning. The condenser I20,shown connected across the relay winding 65, is provided for thispurpose. When the tube 30 is conductive and energizing current flowsthrough the winding 65, the latter will not become magnetically strongenough to cause clockwise rotation of the armature 66 until thecondenser I20 becomes charged. The relay 6|, therefore, will not becomere-energized immediately upon the appearance of a flame at the pilot andconsequently delay in de-energizing the ignition circuit will beintroduced. After a predetermined period of time, depending upon thecapacity of condenser I20, the condenser will become charged andsufficient energizing current will flow through the winding 65 to causeclockwise rotation of the armature 66 and subsequent energization of therelay 6|, and thereby deenergization of the ignition circuit. Bychoosing a condenser of suitable capacity any desired time delay can beobtained and the action of the ignition interrupting means can bedelayed until there is a certainty that the pilot flame is burningsteadily.

If, for any reason, the pilot burner should not become lighted, thepotential of grid 32 will not be raised sufficiently to causeenergization of relays 60 and BI. The result will be that the lasttraced holding circuit for relay coil 85 will not be established and thecurrent flowing therethrough must pass through the heater winding 22.After a predetermined period of time, this will cause the bimetallicelement 20 to;be heated sufliciently to result in a separation of switcharms I3 and I9. The separation of the switch arms opens the circuit tothe primary winding l6 of transformer I1 and de-energizes the entiresystem. As was previously noted, the switch arms I8 and I9 cannotbe-automaticaliy reset so that it is necessary for an attendant toinvestigate the condition which prevents ignition of the pilot burnerbefore the'system can again be put into operation.

Moreover, since itjS necessary for the relay 6i to be energized andde-energized, before the relay 63 can be energized, which last.mentioned relay controls the ignition of the pilot fuel supply,

there is assurance that there will be no faultycheck of the presence ofcombustion due to the presence of a low resistance path betweenelectrode I I2 and the pilot'burner 4. If such acondition should exist,the relay 6| would not be deenergized, so that relay 63 would not beenergized damage thereto.

and the fuel supply and ignition means would not be brought intooperation.

As was mentioned previously, if a condition simulating combustion shouldbe established after the system is in operation, the system will opcrateto close the main fuel supply valve. If a low resistance path isestablished between electrode H2 and the pilot burner 4 after the systemis already in operation, the potential on the grid 32 will be increasedsufiiciently in the positive direction to cause the flow of currentbetween the grid and cathode of the tube 30. This grid current will flowthrough the winding 64 of the relay 60 but will not flow through thewinding 65 so that the former will be made stronger magnetically thanthe latter and the armature 66 will be rotatedin a counter-clockwisedirection, resulting in' separation of the switch arm 10 and contact II.The relay 6! will then be de-energized and the thermal safety switch I5will subsequently operate to de-energize the system.

The circuit through which grid current flows when the electrode H2 isconnected through a low resistance path to ground, may be traced fromthe positive side of condenser 5|, conductor 35, ground connection H6,ground connection II5, electrode II2, conductor II3, resistor H4,conductor 42, grid 32, cathode 33, conductor 31, conductor 98, relaywinding 64, and conductor 99 to the negative side of condenser 5|. Inthe use of the present invention, under certain conditions, it has beenfound desirable to so establish the circuit constants of the system suchthat when the resistance between the flame electrode H2 and ground is10,000 ohms or less, grid current will flow and the'relay 60 will beoperated to de-energize the relay 6|. so operated, the resistance II4should have a value of at least 25,000 ohms in order to limit the flowof grid current in the tube 30 to prevent It is also desirable from acircuit operating standpoint-that the grid current flow between the grid32 and cathode 33 be limited because if this is not done, the grid willbecome hot and will become an emitter'of electrons. These electrons willtravel to the anode 3I and additional current will thereby flow in therelay winding 65. The result will be that additional current will flowin both of the windings 64 and 65 and the operation of the relay 60 willbe unstable. By limiting the flow of grid current in the tube 30,however, this condition is obviated and the system is extremely stablein-operation.

It will be noted that means have been provided for thoroughly testingthe operation of the combustion control system before the establishmentof combustion producing conditions, and after combustion has beenestablished. Thus, if, as a result of carbonization of the electrodes,or direct connection of the electrodes to ground, an abnormal conditionexists before the main fuel valve is open, the main fuel valve will notbe opened and the system will be rendered inoperative. If the electrodeis connected to ground through direct connection or because of excessivecarbonization after the system is already in operation, the system willimmediately detect this abnormal condition and operate to close the mainand pilot fuel valves.

Moreover, assurance is had that there will be no. delay in checking thepresence of a flame preparatory to-shunting of the thermal safetyswitch, by reason of the time required to heat the filaments in tubes 30and 43. Before the re- When the system is- I a pair of diode anodes 34A.

lay 62 can be energized, it is necessary for relay 6| to be energizedand this cannot take place until the filaments are heated. By thusrequiring energization and de-energization of the relay 6| whichultimately-is energized to shunt out the thermal safety switch, meanshave been provided for guarding against a condition which might arisethrough a shorted electrode wherein the thermal safety switch would beshunted out even though ther'ejwas no combustion with the result thatthe ignition and fuel supply means would continue in operation withoutcombustion of the fuel being supplied taking place. Moreover, means havebeen provided for checking the operation of a component part of thesystem. If the tubes 30 and 43 are not funcgoning properly, for example,if the filaments burn out, the relay 6| will not be energized. If thetubes 30 and 43 should be functioning properly, but the resistanceacross the flame gap should be sufliciently low that the flame checkingmeans might otherground'while the system is in operation remainsundetected. It will be noted that if carbonization of the electrode 2occurs to a suflicient degree to reduce the resistance between theelectrode and ground to a value of approximately 10,000 ohms that thesystem will operate to close the main fuel supply valve. The presence ofother abnormal conditions producing the same low resistance path fromthe flame electrode will operate in a similar manner to de-energize thesystem. It is thus seen that the system may be proportioned .so thatslight variations in the conwill not be initially de-energized so that'65 is connected from the positive side of the condenser 5| to the anode3|A through th conductor |2| which has a resistor 96A inserted therein.The purpose of the resistor 96A is to limit the flow of plate current inthe tube 30A.

The relay winding. is connected over conductor I22 from the positiveside of.the condenser 5| overlconductor |23.to;the screen MC. The diodes34A are connected to conductor 36 to one terminal of thetransformer'secondary winding '25 and the other terminal of the winding25 is connected by the conductor 35 to one terminal of the condenser 38.The other terminal of the condenser is connected to conductor 31 to thecathode 33A. The condenser 38 has impressed across its terminals a,pulsating direct current voltage produced by the diode unit, thepulsations of which are filtered out by the condenser. The grid 32Aisconnected through resistor 4| to the negative terminal of condenser 38by the conductors 39 and 42 so that the tendency of the voltage producedby the rectifying action of the diodes 34A is to bias the grid 32Anegatively.

The rectifier 43 of Fig. 2 is identical with the correspondinglyidentified rectifier tube of Fig. 1 and is connected in an identicalmanner through the transformer secondary winding 26 to the opp'ositeterminals of the condenser 5|. Thus a pulsating direct current voltageis maintained across the condenser 5|, the pulsations of which arefiltered out by the condenser The two power supplies are connected inseries, as in Fig. 1, through a conductor I24 which connects thenegative terminal of condenser 5| with the positiv terminal of condenser38. The grid 32A is connected through resistor. 4 and the flameresistance to the positive terminal of the condenser 5| by conductor 95so that the tendency of the ductivity of th flame will not cause thesystem to be de-energized, but if the resistance from the electrode toground decreases to an abnormally small value the system will bede-energized.

In 2, I have illustrated, more or less diagrammatically, a modificationof a portion of the .device of Fig. 1. In this modification, the relay60 is not actuated in response to an abnormal condition by virtue of theflow of grid current,

as in Fig. 1, but in other respects the operation of this device may beidentical with the operation of the device of Fig. '1 For purposes ofsimplification, only the relay 6| has been shown in Fig. 2 and theresistance of Fig. 1 and the circuit for shunting out the latter hasbeen omitted. It

will be understood, however, that thedetection unit shown in 2 may beconnected in the control circuit 01' Fig. 1 and operated in theidentical manner in'which the detection imit of Fig. 1 is operated.

,Referring to Fig. 2, it will be noted that the duplex-diodeetriode 30of Fig. 1 has been replaced by a duplex-diode-pentode type tube 30A.Tube 36A includes an anode 3|A, a cathode 33A, a grid.

32A, a screen C, and :a suppressor grid B. The tube also includes acathode heater 29A and Since only halfwave' rectification is required,the anode diodes 34A may be connected to each other as in Fig. 1. The

voltage across the condenser 5| is to reduce the negative bias on thegrid 32A which is applied thereon by the condenser-38. As in Fig. 1 afurther connection may be provided between the grid 32A and the positiveside of condenser 5| through switch blade 83 and. resistor 93.

1 The checking operations of the device of Fig. 2 preparatory tocombustion may be identical with those described in connection with Fig.1, and hence, require no further description. If an abnormal conditionshould occur after the system is already in operation, the devic of Fig.2 will operate to de-energize the combustion system. When a normal flamebridges the gap between the pilot 4 and electrode 2, the negativepotential maintained on the grid 32A by the condenser 38 will be reducedand space current will be conducted by the tube 30A. With this potentialmaintained on the grid 32A, most of the space current will flow to theanode BIA so that greater current will flow in the winding of the relay60 than in the winding 64, 60 for clockwise rotation. The switchblade"'|0 will then-engage the contact 1| to close an energizing circuitto the relay 6|. The area of the suppressor grid H3 is connected to thecathode 33A in the usual manner, and functions to prevent the flow ofsecondary electrons from the anode MA to the screen 4|B. The relaywinding screen 4|C,.and the suppressor grid 4|B prevents the flow ofsecondary electrons from the anode '3IA to the screen C so that normallymost of the space current will flow to the anode and thereby to thewinding 65. I

- If the resistance of the path from the electrode 2 to ground, however,should decrease to a value approximating 10,000 ohms as a result ofcarbonization of the electrode 2 or any other abnormal condition, thegrid 32A will be connected through a much lower resistance to the andenergize the relay positive side of the condenser and accordingly thepotential thereon will be driven in the positive direction. Because ofthe presence of the current limiting resistor 96A in the anode circuit,the resulting increase in space current will not materially increase theflow of current through the winding 65, but will flow in the screencircuit through the relay winding 64. The relay winding 66 will thenbecome stronger magnetically than the winding 65 and the switch blade I0accordingly will be rotated out of engagement with the When'inoperative, and to thereby prevent atomized fuel from being supplied tothe furnace when the conditions of combustion are not proper. Thecombustion responsive units disclosed in Figs. 3 to 6 may be connectedin the control circuit of Fig. .1 and will function in a similarimannerto that in which the flame detection unit in Fig. 1 functions, to checkthe conditions Jbf combuse tion before permitting the fuel valve to beopened and after the condition of combustion have been established tocontinuously check the resistance from the flame electrode 2 to ground,and upon the occurrence of an abnormally low resistance therebetween torender the system inoperative. In Fig. 3, I have shown the relay 6|connected in the anode circuit of an electronic valve 30,

which may be identical with thecorrespondingly identified valve 30 ofFig. 1, and have provided an additional relay I60 in series with therelay 6| which operates upon the establishment of an abnormally lowresistance from the flame electrode to ground to de-energize the system.The

relay I60 is a sub-sensitive relay and in the normal operation of thesystem suflicient current does not flow therethrough to cause it to beenertrode to ground decreasing to a certain'predetermined low value, theincreased positive potential on the grid 32 will result in increasedspace current being conducted by the tube 30. This increased spacecurrent will cause energization ofthe relay I60 and the latterwilloperate tor move the switch blade |6I out of engagement with thecontact I62, and to thereby open the circuit initially closed byengagement of the switch blade 15 and contact Bil. Opening of thecircuit through contact 80 and switch blade l5 removes the shuntconnection from the heater winding 22, and subsequent heating of thelatter operates to separate the switch members l8 and IQ of the thermalafety switch I5 and to thereby render the system inoperative,simultaneously closing the pilot and main fuel valves.

In Fig. 3, a condenser IZUA is shown connected across the terminals ofthe relay winding 72, the function of this condenser being identicalwith that of condenser I2ll connected across relay winding 65 in Fig. 1.After the conditions necessary for combustion have been established anda'flam'e appears at the pilot, the negative potential on the grid 32will be reduced and the tube 30 will be rendered conductive. 'Due to.the presence of condenser I2IlA the relay winding 6| will not beenergized immediately, but a delay depending upon the capacity of thecondenser will be introduced. The extent of this delay is directlydependent upon. the time required to charge the condenser I20A. As soonas the condenser becomes charged, the relay 6| will be energized andwill operate in the desired manner.

In Fig. 4 an alternative circuit has been disclosed for rendering thecombustion system inoperative when the resistance of the path from theflame electrode to ground reaches a predetermined low value.Forsimplification only, the flame detection circuit i shown in Fig. 3,but it will be understood that this circuit may be connected in thecircuit of Fig. 1 and made to pergized. The relay I60 is operativelyassociated with a switch blade I6I which is biased in any suitablemanner when the relay is de-energized, into engagement with a contactI62. The switch blade |6| and contact I62 are preferably connected inseries circuit relation with the switch blade 15 and contact 80 of therelay 6| of Fig. 1. Referring to Fig. 1 it will be seen that closure ofthe switch arm I5 and contact 80 establishes a shunt circuit across theheater winding 22 of the thermal safety switch I5, and preventsenergization of the latter in normal operation.- By employing the flameresponsive unit of Fig. 3 in conjunction with the control relay circuitof Fig. 1, it will be noted that the occurrence of .a path of apredetermined low resistance between the electrode 2 and ground willresult in separation of the switch blade I6| and contact I62 and therebyremoval of the shunt acros the thermal safety switch heater winding 22.

When normal flame resistance exists from electrode II2 to ground, theflow of space current in the tube 30 will be sufllcient to causeenergization of the relay 6|, but will be ins'uflicient to causeenergization of the relay I60. If an abnormal condition occurs, however,resulting in the resistance of the path from the flame elecform thecombustion checking operations performed by the corresponding flamedetection unit of Fig. 1.

Referring to Fig. 4, a sensitive relay I65 is connected in circuitbetween the grid 32 and the flame electrode II2. Upon the occurrence ofan abnormally low resistance path between the flame "electrode andground, a high positive voltage will be applied to the grid 32,resulting in the flow of grid current in the tube 3|]. This grid currentwill flow through the sensitive relay winding I65 and energize thelatter. A shown in Fig. '4, the relay I65 is operatively associated witha switch arm I6| which is biased into en-'- gagementwith a contact I62when the relay is de-energized. The switch blade I6I and contact I62 areconnected in series with the switch blade I5 and contact 80, as are thecorrespondingly identified parts of Fig. 3, so that energization of therelay I65 and consequent separation of the switch blade |6| and contactI62 results in removal of the shunt across the thermal safety switchheater winding 22 and thereby de-energization of the system.

In Fig. 4, the resistance H4 of Fig. 1 has been omitted, the winding I65of the sensitive relay being ubstituted therefor. When an auxiliaryresistance'such as the resistance H4 is not usedin conjunctiontherewith, the resistance of the winding I65 is preferably madesufficiently high to limit the flow of grid current through the tube 30.If desired, however, an auxiliary resistance, preferably lower in valuethan the resistance Ill since the relay winding I65 necessarilycomprises a resistance, may be connected in series with the relaywinding I65, the combined resistance being employed to limit the flow ofgrid current.

In Fig. 5, I have illustrated another form of the invention in whichmeans are provided for rendering the system inoperative upon the'occurrence of an abnormal condition at the flame electrode. By theutilization of a novel switching arrangement, a material reduction inequipment, necessary for detecting the presence of an abnormally lowresistance path from the flame electrode to ground may be effected.Referring to Fig. it will be noted that only a single relay, which maybe the relay 6|, is required. The relay 6! is operatively associatedwith switch arms 14, 15, and 16 which may be identical with thecorrespondingly identified parts in Fig. 1. For purpose ofsimplification only the relay arm .has been shown in Fig. 5, the circuitde-energizing means being effected by separation of this arm from itsrespective contact 80 as in the previously described forms. The novelswitching arrangement referred to includes two switch blades- 15 andI63. The switch blade 15 is operatively associated with the relaywinding 12, and is adapted upon energization of the latter to be movedinto engagement with the contact 80. When the relay wind- .ing 12 isde-energized the switch blade 15 is biased out of engagement with thecontact 60. The contact 60 is carried by the second mentioned switchblade I63 and the latter is biased in any. suitable manner intoengagement with a contact I 62'. Before combustion has taken place and aflame has appeared at the pilot, a high negative. potential will beapplied to the comes greater than the bias urging the switch blade I63into engagement with the contact I62, the latter mentioned parts will beseparated.

By properly designing the switch blade I63 and current flow from thisgrid 32 and negligible current will be conducted by the tube 30. Theswitch arm 15 will then be biased out of engagement with the contact'86. Upon the appearance of a flame, however, the negativepotential onthe grid 32 will be reduced and space current of'a predetermined normalvalue will be conducted by the tube 30. The switch arm 15 will then bemoved into engagement with the contact 80. The bias urgingthe switchblade I63 into engagement with the aforementioned contact I62 ispreferably of such value that the force exerted on the contact 66 by theswitch arm 15, with normal flow of current through the relay winding 12,is insufficient to pull switch blade I63'.out of engagement with thecontact I62 but upon an abnormally large current in winding 12 blade I63will be separated from contact I62.

It is thus sen that with proper conditions of combustion that'a circuitis closed from conductor I02 to conductor H9, and by reference to Fig. 1it will beseen that the closure of this circuit V effectively shunts thethermal safety I switch heater. winding 22. The latter is therebyprevented fromoperating to de-energize the system and normal operatingconditions have been established. k

If a' high positive potential is applied to the grid 32, as a result ofthe presence of an abnormally low resistance.path from the flame elec'trode to ground,'however, increased space current will be conducted bythe tube 30,- and this increase in current in winding 12 will result inthe latter becoming stronger magnetically. The

switch blade 15 will then be urged with greater force into engagementwith thecontact 80 and when the pull exerted by relay winding 12 bee )7current.

the means biasing it into engagement with the contact I62, it is thusseen that the relay 6| may be made to operate to open this contact whena predetermined value of current is flowing in the winding 12, andthereby when a path of predetermined low resistance has been establishedfrom the flame electrode II2 to ground.

As in the previously described forms of my invention, opening of thecircuit shunting the in the. latter operating to de-energi'ze thesystem.

It will be clear therefore that with a current value in the anodecircuit of valve 30 which'is position on a low anode current value, to asecond'positionon an intermediate current value and to the firstposition on a higher plate current value. Such relay operation is'useful in various connections including those illustrated herein. Thusthere is a range of current fiow in the anode circuit of valve 30 or inother words a band of predetermined width which is directly dependentupon the relative forces biasing the switch arms 15 and I63 in anupwarddirection wherein the fuel supply to the furnace is permittedand uponany departure of the anode predetermined range the relay 6| is caused tooperate in a sense to cut off the supply of fuel to the furnace.

In Fig. 6, a further modification of my invention has been illustratedin which the increased flow of space current conducted by the tube 36.as a result of the presense of an abnormally low resistance path fromthe flame electrode to ground is utilized to blow a fuse which may beconnected in the anode, cathode, or grid circuit of the tube 30'asdesired, and tothereby cause de-energization of the system. For purposesof explaining theoperation of this modification of my invention, I havein the anode circuit of the tube 30.

Referring to Fig. 6, the above mentioned fuse is shown designated by thereference character I10 and is connected in series with the relaywinding 12. When normal conditions of combustion are prevailingand-aflame is present at the pilot, the space current conducted by thetube 30 will be a predetermined value which is suflicient for the normaloperation of the relay 6|. The fuse I10 adapted to easily withstand thisflow of anode If a high-positive grid 32. in space thermal safety switchI5 to operate to render. the system inoperative.

The required rating for the fuse I16 will necshown the fuse connected isof such rating that it ispotential is applied to the however, causing asubstantial increasecurrent conducted by the tube 36, the

ti e

essarily depend upon its location in the circuit as seen in Fig. 6. Theanode current conducted by the tube 30 may be different from the currentin the cathode circuit, depending upon whether or not grid currentis'flowing in the tube, and hencethe current ratings of a fuse for eachof these circuits should be of corresponding values. The current whichit is desirable to permit to flow in the grid circuit of the tubeisnecessarily much less than the anode or cathode current, and hence, if afuse is placed in the grid circuit, it must be so designed as to blow ata correspondingly low value or current therethrough.

In Fig. 7, I have illustrated, more or less diagrammatically, anothermodification of my invention which may be employed in checking thecombustion conditions of a plurality of fuel fired furnacessimultaneously. Although it will be understood that the flame responsiveunits of Fig, 7 may be employed in conjunction with the controlrelaysystem of Fig. 1, I have, for purposes of simplification, shownthis form of my invention as adapted to be employed in conjunction withmanually lighted furnaces. When so employed, the circuit of Fig. '7 willoperate upon flame failure, or upon the occurrence of an abnormally lowresistance path to ground, from any one of the flameelectrodesassociated with the respective burners, due to accidentalshorting or carbonization or for any other reason, to close the mainfuel supply valve or to maintain said fuel valve closed if any one ofthe burners fails to ignite.

in the manner described in connection with Fig.

1 so that the space current conducted by the tube 30 upon the appearanceof' a flame at the pilot results in actuation of the corresponding relay80 and thereby movement of the switch blade I0 into engagement with thecontact II. Allthe contacts '|0-'II are in series so that when a pilotflame has appeared at each of the burners and each of the relays 60 hasoperated to close its respective contact II, a circuit will have-beencompleted, through the switch blades I0 and contacts 'II, to a relayI90. This circuit may be traced from one end of the transformersecondary winding 24, conductor I22, switch blade 10 and contact II ofthe first relay, conductor 83 switch blade 10 and contact 'II of thenext relay, conductor 63 relay winding I90, and conductor 13 to theother end of thetransformer secondary winding 24. The relay windingI90-is operatively In Fig. 7, in order to avoid confusion of thedrawings, I have shown a circuit responsive to the combustion conditionsof only two fuel fired furnaces, but it will be understood that four orfive fuel fired furnaces may be so controlled from a single controlunit, the only limit as to the actual number of furnaces which may be socontrolled being the load that the transformer I1 can safely handle.

While any suitable means may be employed for lighting the burners, forexample, the control system described in connection with Fig. l, forclearness and definiteness of illustration, I have shown an arrangementin Fig. 7 wherein the pilot and main flames may be lighted as the resultof a manual operation, and after combustion has taken place the systemwill operate so as to maintain the pilot and main fuel valves in openposition.

The arrangement referred to above includes a plurality of ignitiontransformers 8, each associated with a respective pilot burner, andadapted to be energized together with the pilot valve actuating meansupon closure of a normally open push button I80. The energizing circuitfor the pilot valve actuating means may be traced from the supply line Lconductor I05, push button I80, conductor I8I, the pilot valve actuatingmeans-and conductors I84 and H0 to the supply line L "and theenergizingcircuit for the igni-' tion transformers may be traced from the supplyformers 8,- which may desirably be connected in associated with a pairof switch arms HI and I94 which are adapted upon energization of therelay winding to be moved into engagement with contacts I93 and I95,respectively, but when the relay winding is deenergized, are held out ofengagement therewith, and the switch blade I9I is then held intoengagement'with contact I92.

The switch arm I94 and contact I95 are included in an energizing circuitto the main valve actuating means so that energization of the relaywinding I90 resultsin the establishment of a circuit for actuating themain fuel valve to its open position. This circuit may be traced fromthe supply line L, conductor I08, switch blade I94, contact I95,conductor I85, the main fuel valve actuating means, and conductor H0 tothe supply line L The switch blade I9I and contact I93 are included inan energizing circuit to the pilot-valve actuating means, independent ofthe push button energizing circuit, so that energization of the relaywinding I90 results in the establishment of a holdingcircuit for thepilot valve actuating means which may be traced from the supply line Lconductor I06, contact I93, switch blade I9I, the pilot valve actuatingmeans and conductors I84 and IIO'to the supply line L Furthermore, itwillbe noted that when the relay 7 winding I90 is energized, theenergizing circuit to the ignition transformers 8 is interrupted, andthereby the ignition transformers are deenergized, as a result ofseparation of the switch blade I9l and contact I92. The operatingcondition .of the circuit having thus been established, the push buttonI80 may subsequently be released.

The system will then continue to operate, as long as the conditions ofcombustion are proper, so long as it'is desired to maintain the burnersin operation. For interrupting the energizing circuit to the pilot andmain fuel valve actuating means when it is desired to shut down-thesystem, means have been provided in the form of 2. normally closed pushbutton I96. The latter may be ....inserted in the energizing conductorI08 and opparallel, and conductor I83 to the supply line L.

As soon as a pilot flame. appears at one of the burners the negativebias on the grid 32 of the tube 30 is reduced and the tube is i Thetubes 30 are each oprespective rendered conductive. v erativelyassociated with a respective relay 80 and the individual flame detectionunits operate erates when actuated so as to result in closure of thepilot and main fuel valves and thereby the shutting off of the fuelsupply to the various burners. As soon as one of the pilot flames isextinguished, the corresponding tube 30 becomes non-conductive and therelay which cooperates therewith is ole-energized. This results ininterruption of the energizing circuit to the relay winding I andthereby separation of the switch blades I9! and I94 and their respectivecontacts I93 and I95. If thereafter, the push button I96 is released andlater closed the system will remain de-energlzed until'switch I80 isclosed.

second v wound on the same core, only one primary wind- If, while thesystem is in operation, one of the electrodes H2 should he accidentallyconnected to ground or should be connected to ground through anabnormally low resistance by reason of carbonization or for any otherreason, the detection unit individual thereto will immediately detectthis condition and operate to cause deenergization of the entire system.The operation of each of the detection units upon the ocurrence of suchan abnormal condition may be identical with that described in connectionwith Fig. 1, and

. cult of the tube 30, but not in the anode circuit thereof, resultingin greater current flow through the winding 64 than through the winding65 of the corresponding relay 60. The result is that the armature 68 is'so rotated as to move the switch blade 10 out of engagement with thecontact H and the energizing circuit to the relay winding ISO isinterrupted, causing the pilot and main fuel valves to be closed. A

In Fig. 7 two individual power supply transformers l1 and "A have beenshown, the primary windings of which are energized from the adapted tobe bridged by the burner flame, a relay having a normally open contactconnected in circuit with said cathode, anode, and said source ofenergizing current, a second relay having a normally closed contactconnected in circuit with said cathode, control grid, flame electrodeand said source of energizing current, circuit means including saidrelay contacts adapted upon closure of said first mentioned contact tocause said burner fuel control means to assume a fuel feeding position,and adapted upon opening of said second mentioned contact to cause saidburner fuel control means to assume a position preventing the supply offuel.

3. In a burner control system, a burner, burner fuel control means, anelectronic valve including an anode, a cathode, and a control grid, anelectrode located near but separated from said burner by a gap adaptedto be bridged by the burner flame, a connection between said electrodeand said control grid, circuit control means including said cathode andanode adapted to cause said burner fuel control means to assume a fuelfeeding position, and circuit control means opposing said flrstmentioned circuit control means and including said cathode and controlgrid adapted to cause said burner fuel control means to assupply linesL' and L. If desired, however, the V windings of these transformers maybe ing being employed. It will be readily understood that by' employingseparate transformers for the various energizing circuits of Fig. 7 thatthe number of burners which may be operated from a single control unitmay be increased.

Whilein accordance with the provisions of the statutes, I haveillustrated and described the best form of embodiment of my inventionnow known to me, it will be apparent to those skilled in the art thatchanges may be made in the form of the apparatus disclosed withoutdeparting fromthe spirit of my invention as set forth inthe appendedclaims and that in some cases certain features of my invention may beused to advansume a position preventing the supply of fuel.

4.111 a burner control system, a burner, burner fuel control means, anelectronic valve including an anode, a cathode, and a control grid, anelectrode located near but separated from said burner by a gap adaptedto be bridged by the burner flame, a connection between said electrodeand said control grid, circuit means including said cathode and anodeadapted to cause said burner fuel control means to assume a fuel feeding position in response to the increased conductivity of the gapbetween said electrode and said burner by reason of the burner flamebridg -said gap. and circuit means opposing said first tage without acorresponding use of other fea- 7 cures.

Having now described my invention, what I claim as new and desire-tosecure by Letters Patcut, is:

i. In a burner control system, a burner, burner fuel controlmeans, anelectronic valve including a cathode, an anode and a control grid,energizing means, an electrode located near said burner butseparated'therefrom by a gap adapted to be bridged by the burner flame,a connection between said electrode and said control grid, relay meansconnected in circuit with said cathode and anode and said energizingmeans tgdaplglexd t: cause said burner fuel control means ass e fuelfeeding position when said gap is bridged by the burner flame, and relaymeans connected in circuit with said cathode and control grid and saidenergizing means adapted to cause said burner fuel control means toassume a position preventing the supply offuel when an abnormal leakagepath has been established between said electrode and ground. 7

2. In a burner control system, a burner,-burner fuel control means, anelectronic valve including a cathode, an anode and a control grid,asource of energizing current, an electrode located near said burner butseparated -therefrom by a gap mentioned circuit means and including saidcathode and said control grid adapted to cause said burner fuel controlmeans to assume a position preventing the supply of fuel in response tothe conductivity of the gap between said flame electrode and burnerbecoming abnormally high. 5. Inc. burnercontrol system, a burner, burnerfuel control means, an electronic valve including an anode, a cathode,and a control grid, an elec-' trode located near but separated from saidburner by a gap adapted to be bridged by the burner flame, a connectionbetween said electrode and said control grid, a relay having two opposedwindings, one of which is wound with more turns. than. the other,circuit means including a current limiting resistor in series with'saidcathode and anode and both of said opposed windings for feeding means,and circuit means including said cathode and control grid and the relaywinding wound with the fewer turns for actuating said relay tode-energize said burner fuel feeding means.

6. In a burner control system, a burner, burner fuel control means, anelectronic valve having a plurality of elements, an electrode locatednear but separated from said burner by a gap adapted to be bridged bythe burner flame, a connection between said electrode and one of theelements of said valve, a relay having two opposed windings, one ofwhich is wound with more turns than the other, circuit means includingtwo other elements of said valve and both of said opposed windingsvalues, an electronic valve including an said device and said controlcathode. and anode for actuating'said: relay to energize said burnerfuel feeding means, and circuitmeans including at least one of the lastmentioned elements of said valve and another element and therelaywinding wound with the fewer turns for actuating' said-relay to'de-energize said burner fuel feeding mean-s; g

I. In a burner control system, a'burner, burner fuel control means, anelectronic valve including an anode, a cathode, and a control grid, anelectrode located-near but separated from said burner by a gap adaptedto be bridged by the burner flame, a connection between said electrodeand said control grid, a relay having two'opposed windings, one of whichis wound with'more turns than the other, circuit means including saidcathode and anode, and both of said opposed windings for actuating saidrelay to energize said burner fuel feeding means, and circuit meansincluding said cathode and control grid and the relay winding wound withthefewer turns for actuating said relay to de-energize said burner fuelfeeding means. a e

8. In a burner control system, a burner, burner fuel control means, anelectronic valve including an anode, a cathode, and a control grid, anelectrode located near but separated from said burner by a gap adaptedto be bridged by the burner flanie, a connection between said electrodeand said control grid, circuit meansincludingsaid cathode and anode andacurrent limiting resistor adapted to cause said burner fuel controlmeans to assume a fuel feeding position, andcircuit means opposing saidfirst mentioned circuit means and including said cathode and controlgrid, and said electrode adapted to cause said burner fuel control meansto assume a position preventing the supply of,fuel.

9. In a burner control system, a burner, burner fuel control means, anelectronic valve including an anode, a cathode, and a control grid, anelectrode located near but separated from said burner by a gap adaptedto-be bridged by the burner flame, a relay having an open position and aclosed position and adapted to control said burner fuel control means inone sense when in said open. position and in an opposite sense when insaid closed position, circuit means for actuating said relay to saidclosed position including said cathode and anode, and circuit meansopposing said first mentioned circuit means for actuating said relay tosaid open position and including said cathode, control grid and saidelectrode.

10. In a control system, burner means'adapted' to cooperate with avariable condition which is adapted to be modified by said burner means,saidcondition normally varying over a predetermined intermediate rangeof values and abnormally adapted to assume two widely displaced values,means for controlling said first mentioned means in one sense tomaintain said condition within said predetermined range of values and inanother sense upon the occurrence of said condition assuming one of saidwidely displaced anode, a cathode, and a control grid, a deviceresponsive to said variable condition, a connection between grid, arelay having two opposed windings, one of which is wound with more turnsthan the other, circuit means including a current limiting resistor inseries with said windings for actuating said relay to control saidcontrol means in said one sense, and circuit means including saidcathode and control grid and the relay winding wound with the fewerturns for actuating said relay to control said control means in saidanother sense. 1

11-. In a control system, burner means adapted to cooperate with avariable condition which is adapted to be modified by said burner means,said condition normally varying over a predetermined intermediate rangeof values and abnormally adapted to assume two widely displaced values,means for controlling said first mentioned means in one sense tomaintain said condition within said predetermined range of values and inanother sense upon the occurrence of said condition assuming one of saidwidely displaced values, an electronic valve including an anode, acathode, and a control grid, 9. device responsive to. said variablecondition, 'a connection between said device and said control grid, arelay having two opposed windings, one of which is wound with more turnsthan the other, circuit means includ ing said cathode and anode and bothof said opposed windings for actuating said relay to'control saidcontrol means in said one sense, and circuit means including saidcathode and control grid and the relay winding wound with the fewerturns for actuating said relay to control said control means in saidanother sense.

12. In a, control system, burner means adapted to cooperate with avariable condition which is adapted to be modified by said burner means,said condition normally varying over a predetermined intermediate rangeof values and abnormally adapted to assume two widely displaced values,

' means for controlling said first mentioned means in one sense tomaintain said condition within,

said predetermined range of values and in another sense upon theoccurrence of said condition assuming one of said widely displacedvalues, an electronic valve including an anode, a cathode, and a controlgrid, a device responsive to said variable condition, a connectionbetween said device and said control grid, a'circuit including saidcathode and anode, a circuit including said cathode and control grid,and means independently controlled by each of said circuits forcontrolling said control means.

13. In a burner control system, a burner, burner fuel control means, anelectronic valve including a cathode, an anode,.a screen grid, and acontrol grid, an electrode located near but-separated from said burnerby a gap adapted to be bridged by the burner flame, a connection betweensaid electrode and said control grid, circuit control means includingsaid cathode and anode adapted to cause said burner fuel control meansto assume a fuel feeding position, and circuit control means includingsaid cathode andsaid screen grid adapted to cause said burner fuelcontrol means to Y assume a position preventing the supply of fuel.-

14. In a burner control system, a burner, burner fuel control means, anelectronic valve including an anode, a cathode, a control grid, and

and both of said opposed a screen grid, an electrode located near butseparated from said burner by a gap adapted to be bridged by the burnerflame, a relay having two, I opposed windings, one of which is woundwith more turns than the other, circuit means including said cathode andanode and a current limiting resistor in series with both of saidopposed windings, circuit means including said cath ode and said screengrid and the relay winding wound with the fewer turns, energizing means,means adapted when the first mentioned circuit is energized to a greaterdegree than the second mentioned circuit to cause said burner fuelcontrol means to assume a fuel feeding position, and means adapted whenthe second mentioned circuit is energized to a greater degree than thefirst mentioned circuitto cause said burner fuel control means to assumea position preventing the supply of fuel.

15. In a burner control system, a burner, burner fuel control means, anelectronic valve including a cathode, an anode, a control grid, and

a screen grid, an electrode located near but separated fromsaid burnerby a gap adapted to be bridged by the burner flame, a connection betweensaid electrode and said control grid, circuit control means includingsaid cathode and anode adapted to cause said burner fuel control meansadapted to be modified by said burner means,

adapted to be modified by said burner means, said condition normallyvarying over'a predetermined intermediate range of values and abnormallyadapted to assume two widely displaced values, means for controlling.said first mentioned means in one sense to maintain said conditionwithin said predetermined range of values and in another sense upon theoccurrence of said condition assuming one of said widely displacedvalues, a device responsive to said condition, an

' electronic valve including an anode, cathode and control electrode, asource of energizing current, a relay having a normally open contactconnected in circuit with said source of energizing current and saidanode and cathode, a relay, having a normally closed contact, connectedin circuit with said source of energizing current, said deviceresponsive to said condition, said cathode and said condition normallyvarying over a predetermined intermediate range of values and abnormallyadapted to assume two widely displaced values, means for controllingsaid first mentioned means in one sense to maintain said conditionwithin said predetermined range of values and in another sense upon theoccurrence of-said condition assuming one of said widely displacedvalues, an-electronic valve including an anode, a cathode, a controlgrid and a second grid, a device responsive to said variable condition,a connection between said device and said control grid, a circuitincluding said cathode and anode, a circuit including said cathode andthe second one of said grids, and means jointly controlled by saidcircuits for controlling said control means.

17., In a burner control system, a burner, burner fuel control means, anelectronic valve including an anode, cathode, and a control grid, anelectrode located near the burner but separated therefrom by a gapadapted to be bridged by the burner flame, a connection between saidelectrode and said control grid, energizing means, a relay adapted tocontrol said burner fuel control means and energized by said energizingmeans under control of saidielectronic valve, said relay having anormally open contact anda normally closed contact and adapted whennormally energized to close said open contact and when abnormallyenergized to close said open contact and to opensaid closed contact,circuit means connected in-series with both of said contacts adaptedupon closure of said open contact to causesaid burner fuel control meansto assume a fuel feeding position and adapted upon opening of saidnormally closed contact to cause said burner fuel control means toassume a position preventing the supply of fuel.

18. In a combustion control system, means for producing combustion,arelay to control said means, an electronic 'valve having a cathode,anode and a control grid, means in circuit with said anode and cathodefor controlling said relay and adapted to control the adjustment of thelatter to one position in response to a predetermined current valuethrough said valve, to a second position in response to another value ofsaid current and to a third position in response to a third value ofsaid current, and means responsive to combustion for controlling saidgrid.

19. In a control system, burner means adapted said control electrode,and means jointly controlled by said relays for controlling said controlmeans.

20. In a control system, burner means adapted to cooperate with avariable condition which is adapted to be modified by said burner means,

said condition normally varying over a predetermined intermediate rangeof values and abnormally adapted to assume two widely displaced values,means for controlling said first mentioned means in one sense tomaintain said condition within said predetermined range of values and inanother sense upon the occurrence of said condito cooperate with avariable condition which is tion assuming one of said widely displacedvalues, circuits including an electronic valve including an anode,cathode and a control electrode, means responsive to said variablecondition -for controlling said electrode to thereby control the an-.

ode current, a relay to control said control means, said relay having awinding included in said anode circuit and having a pair of normallyopen contacts and a pair of normally closed contacts and operating whenboth pairs of contacts are closedto produce operation of said controlmeans in said one sense and operating when one of said pairs of contactsis open to produceoperation of said control means in said another sense,biasing means tending to open the first mentioned contacts, biasingmeans tending to close the second pair of contacts, and means responsiveto a predetermined current of one value in said winding' to overcomesaid first biasing means and close said firstcontacts and responsive toa predetermined current of another value in said winding to overcomesaid second biasing means and open said second contacts.

burners, burner fuel control means, an electrode individual to each ofsaid burners and separated therefrom by a gap adapted to be bridged bythe individual burner flames, an electronic amplifier the control gridsof the electronic valve individual thereto, circuit means including saidanodes and cathodes of saidelectronic valves adapted when the burnerflames bridge said gaps to cause said a burner fuel control means toassume a fuel feeding position and circuit means opposing said firstmentioned circuit means and including said cathodes and control gridsand adapted when an abnormal leakage path has been established betweenone of said electrodes and ground to cause said burner-fuel controlmeans to assume a position preventing the supply of fuel.

21. In a fuel burner system, a plurality of e 2,245,730 I 2i. In acontrol system, burner means adapted to cooperate with a plurality ofvariable conditions, each condition adapted to be modified by arespective one of said burner means, each of said conditions normallyvarying overa predetermined intermediate range of values and abnormallyadapted to assume twowidely displaced values, means for controlling saidfirst mentioned means in one sense to maintain said conditions withinsaid predetermined range or values and in another sense upon theoccurrence of said conditions assuming one [of said widely displacedvalues, a device individual to and responsive to each of saidconditions, an electronic valve individual to eachof said devices, eachof said electronic valves including an anode, cathode, and a,

control grid, connections between each of said control grids and thedevice individual thereto, circuit means including said anodes andcathodes of said electronic valves, circuit means including saidcathodes and control grids, and means jointly controlled by saidcircuits for controlling said control means. V

23. In a control system, burner means adapted 'to cooperate with avariable condition which is 'said predetermined range of values and inanother sense upon the occurrence of said condi-' tion assuming one ofsaid widely displaced values, an electronic valve including an anode, acathode, a control grid and a secondgrid, a device responsive to saidcondition, a connection between said device and said control grid, arelay having two opposed windings, one of which is wound with more turnsthan the other, circuit means including said cathode-and anode in serieswith both of said windings, circuit means including said cathode and oneof said grids and the relay winding wound with the fewer turns,energizing means, means adapted when the first mentioned circuit isenergized to a greater degree than the second mentioned circuit to causesaid control means to operate in said one sense and means adapted whenthe second mentioned circuit is energized to a greater degree than thefirst mentioned circuit to cause said control means to operate in saidanother sense.

24. In a safety control device, burner means adapted to cooperate with avariable condition which is adapted to be modified by said burner means,said condition normally varying over a predetermined intermediate rangeof values and abnormally adapted to assume two widely displaced'values,a motor for controlling said first mentioned means in one sense tomaintain said condition within said predetermined range of values and inanother sense upon the occurrence of said condition assuming one of saidwidely displaced values, a device responsive to variations in the valueof said condition, a connection between said motor and a source ofenergy, apparatus for controlling said motor including a member actuablein one direction for controlling said motor in one sense and actuable inthe opposite direction for controlling said motor in the oppomeans forsaid member, second energizing means for said member, a connection to beenergized responsively to the intermediate one of said values and to bedeenergized responsively toanother of said values and including saidfirst mentioned energizing means and said output circuit, and a secondconnection tobe energized responsively to the third mentioned value andincluding said second mentioned energizing means and said input circuit.

25. In a safety control device, burner means adapted to cooperate with avariable condition which is'adapted to be modifiedby said burner vmeans,said condition normally varying over a predetermined intermediate rangeof values andabnormally adapted to assume two widelyv displaced values,a motor for controlling said first mentioned means in one sense tomaintain saidcondition within said predetermined range of values and inanother sense upon the occurrence of said condition assuming'one of saidwidely displaced values, a device responsive to variations in the valueof said condition, a connection between said motor and a source ofenergy, apparatus for controlling said motor including a member actuablein one direction for controlling said motor in one sense and actuable inthe opposite direction for controlling saidmotor in the opposite sense,said device being responsive to three successive values of saidcondition, means connected to said device for controlling'said memberand including an electronic valve having an anode, a cathode,

'and a control grid, first energizing means for said member, secondenergizing means for saidmember, a connection to be energizedresponsively to the intermediate one of said values and to bedeenergized responsively to another of saidvalues and including saidfirst mentioned ener-- gizing means and the anode and cathode of saidvalve, and a second connection to be energized responsively to .thethird mentioned value and including said second mentioned energizingmeans and the cathode and control grid of said valve.

26. Safety control apparatus for a fuel burner including an electrodeassociated with the burner flame, relay means controlling said burner inone sense to supply fuel thereto and in the opposite sense to interruptsaid fuel supply, an impedance responsive device to control said relaymeans in said one sense when the value of the impedance to which saiddevice is responsive is within a presite sense, said device beingresponsive to three put circuit and an output circuit, first energizingdetermined range of values and in said opposite sense when the value ofthe impedance to which said device is responsive is higher or lower thansaid predetermined range, a connection between said electrode and saiddevice, said impedance including the impedance between said burner andsaid electrode, an additional impedance to control the response of saidimpedance responsive device to said first mentioned impedance, 9.connection between said additional impedance and said device, andswitching means associated with said device and actuated when said relaymeans is actuated in said one sense to render said additional impedanceineffective.

27. The combination of claim 26 in which said additional impedance isinitially effective to control the sensitivity of said impedanceresponsive device and thereby to make said impedance responsive devicecontrol said relay means in said one sense on the occurrence of animpedance path between said electrode and ground higher than apredetermined value and on actuation of said switching means isthereafter ineirective to conbustible agent to produce a combustioncondition and said means are operated to continue the supply of saidagent as long as the value of said condition lies within a predeterminedsafe range of values and said means are operated when said conditionassumes a value without said predetermined range of values todiscontinue the supply 7 of said agent, the combination with said meansof an electronic valve having an anode, a cathode, and a control grid, adevice responsive to the value of said condition, a connection betweensaid device and said control grid, a circuit including said cathode andanode, a circuit including said cathode and control grid, and meansindependently controlled by each of said circuits for controlling saidfirst mentioned means, said controlling means operating said firstmentioned trolling said first mentioned means, said controlling meansoperating said first mentioned means in the sense to supply said agentwhen the control effect on said controlling means of sald'firstmentioned circuit predominates over that of the second mentioned circuitand operating said first mentioned means in the sense to discontinue thesupply of said agent when the control efiect on said controlling meansof said second mentioned circuit predominates over that of the firstmentioned circuit.

' 30. In a safety control system of the class wherein means are providedto supply a combustible agent to produce a combustion condition and saidmeans are operated to continue the supply of said agent as long as thevalue of said condition lies within a predetermined safe range of valuesand said means are operated when said condition assumes a value withoutsaid predetermined range of values to discontinue the supply of saidagent, the combination with said means of an electronic valve having ananode, a cathode, and a control grid, a device responsive to the valueof said condition, a connection between said device means in the senseto supply said agent when the control effect on said controlling meansof said first mentionedcircuit predominates over that of the secondmentioned circuit and operating said first mentioned means in the senseto discontinue the supply of said agent when the control efiect on saidcontrolling means of said second mentioned circuit predominates overthat of the first mentioned circuit.

29. In a safety control system of the class" wherein means are providedto supply a com bustible agent to produce a combustion condition andsaid means are operated to continue the supply of' said agent as long asthe value of said condition lies within a predetermined safe range ofvalues and said means are operated when said condition assumes a valuewithout said predetermined range of values to discontinue the supply ofsaid agent, the combination with said means of an electronic valvehaving'an anode, a cathode, and a control grid, a single deviceresponsive to the value of said condition, a connection between saiddevice and said control grid, a circuit including said cathode andanode, a circuit and said control grid, a relay having two opposedwindings one of which is wound with more turns than the other to controlsaid means, circuit means including said cathode and anode and both ofsaid windings for actuating said relay to control said means in onesense to permit the supply of said agent, and circuit means includingsaid cathode and control grid and the relay winding wound with fewerturns for actuating said relay to control said meansin another sense todiscontinue the supply of said agent.

31. Apparatus for controlling a burner to ensure safe operation thereofincluding means responsive to a-predetermined range of resistance valuesof a path normally including theburner flame, means to ignite theburnerif said resistance is higher than the maximum value of saidpredetermined range of values, said respon sive means includingmeansresponsive to the resistance of said path and operative thereafterto prevent the operation of said burner if .said resistance falls belowor rises above said predetermined range of values.

HUBERT T SPARROW.

